Due to their abundance, high strength and stiffness, low weight and biodegradability, nano-scale cellulose fiber materials (e.g., microfibrillated cellulose and bacterial cellulose) serve as promising candidates for bio-nanocomposite production. Such new high-value materials are the subject of continuing research and are commercially interesting in terms of new products from the pulp and paper industry and the agricultural sector. Cellulose nanofibers can be extracted from various plant sources and, although the mechanical separation of plant fibers into smaller elementary constituents has typically required high energy input, chemical and/or enzymatic fiber pre-treatments have been developed to overcome this problem. A challenge associated with using nanocellulose in composites is the lack of compatibility with hydrophobic polymers and various chemical modification methods have been explored in order to address this hurdle. This review summarizes progress in nanocellulose preparation with a particular focus on microfibrillated cellulose and also discusses recent developments in bio-nanocomposite fabrication based on nanocellulose.

Microfibrillated cellulose and new nanocomposite materials: a review

Physical and mechanical properties of PLA, and their functions in widespread applications - A comprehensive review.

Poly(lactic acid) (PLA), so far, is the most extensively researched and utilized biodegradable aliphatic polyester in human history. Due to its merits, PLA is a leading biomaterial for numerous applications in medicine as well as in industry replacing conventional petrochemical-based polymers. The main purpose of this review is to elaborate the mechanical and physical properties that affect its stability, processability, degradation, PLA-other polymers immiscibility, aging and recyclability, and therefore its potential suitability to fulfill specific application requirements. This review also summarizes variations in these properties during PLA processing (i.e. thermal degradation and recyclability), biodegradation, packaging and sterilization, and aging (i.e. weathering and hygrothermal). In addition, we discuss up-to-date strategies for PLA properties improvements including components and plasticizer blending, nucleation agent addition, and PLA modifications and nanoformulations. Incorporating better understanding of the role of these properties with available improvement strategies is the key for successful utilization of PLA and its copolymers/composites/blends to maximize their fit with worldwide application needs.

Physical and mechanical properties of PLA, and their functions in widespread applications — A comprehensive review

Green composites from sustainable cellulose nanofibrils: A review

Poly(lactic acid)-Mass production, processing, industrial applications, and end of life.

Poly(l-lactic acid) (PLLA) samples were prepared with different degrees of crystallinity, obtained during cooling from the melt at different scanning rates, and subjected to annealing below Tg. For intermediate crystallinities two endothermic peaks assigned to enthalpy recovery could be detected by differential scanning calorimetry (DSC) on heating, indicating the existence of two distinct glass transition dynamics. The morphology at different length scales was characterized using WAXS, SAXS, and polarized light microscopy to correlate the DSC results to the microstructure. The low-temperature process was assigned to the bulklike glass transition whereas the high-temperature one was attributed to the restricted motions of the amorphous phase confined by the crystalline structures. The position and broadness of the two endotherms were found to be essentially independent of the spherulitic content of the samples. This was related to the invariance of the lamellar morphology within a large range of degrees o...

Morphological contributions to glass transition in poly(L-lactic acid)

In-line monitoring of the thermal degradation of poly(l-lactic acid) during melt extrusion by UV–vis spectroscopy

The cold crystallization process of initially amorphous poly(L-lactic acid), PLLA, with two different molecular weights, during a heating at 2°C/min, was investigated by DSC and time-resolved simultaneaous SAXS and WAXS, using synchrotron radiation. Equatorial scans of the isotropic 2D-SAXS patterns showed that the average Bragg long period (L B ) of PLLA samples was approximately constant with the development of cold crystallization up to a temperature that corresponded to a melt/re-crystallization process that took place before the nominal melting peak seen by DSC. L B values were found to be higher for the high molecular weight material. This was in accordance with the higher melting temperature observed in the high molecular weight PLLA that implied the existence of thicker lamellae. WAXS results showed that the molecular weight did not apparently affect the crystal form and the final degree of crystallinity of PLLA. The Avrami parameters from WAXS and DSC were consistent, showing that the non-isothermal cold crystallization of the two PLLA samples corresponded mainly to a three-dimensional growth, although an imperfect crystallization rate of PLLA, observed both by WAXS and DSC, decreased with increasing molecular weight.

Cold Crystallization of PLLA Studied by Simultaneous SAXS and WAXS

Flexible polyvinylidene fluoride film with alternating oriented graphene/Ni nanochains for electromagnetic interference shielding and thermal management

Polycaprolactone (PCL) and starch/PCL blends (SPCL) are shown to have the potential to be used in a range of biomedical applications and can be processed with conventional melting-based procedures. In this paper, the thermal and thermomechanical analyses of PCL and SPCL were performed, using DSC, optical microscopy and DMA. Starch effectively increased the non-isothermal crystallisation rate of PCL. Non-isothermal crystallisation kinetics was analyzed using Ozawa model, and a method, which combines the theories of Avrami and Ozawa. Starch effectively reinforced PCL and enhanced its damping properties, which indicated that SPCL could be more suitable than PCL in some biomedical applications, as it might help in the dissipation of the mechanical energy generated by the patient movements.

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Yaming Wang

Papers

Morphological contributions to glass transition in poly(L-lactic acid)

In-line monitoring of the thermal degradation of poly(l-lactic acid) during melt extrusion by UV–vis spectroscopy

Cold Crystallization of PLLA Studied by Simultaneous SAXS and WAXS

Flexible polyvinylidene fluoride film with alternating oriented graphene/Ni nanochains for electromagnetic interference shielding and thermal management

Thermal and Thermomechanical Behaviour of Polycaprolactone and Starch/Polycaprolactone Blends for Biomedical Applications